How well your lungs put oxygen into and remove carbon
dioxide from your blood.

Types of lung function tests include:

Spirometry.

Gas diffusion.

Body plethysmography.

Inhalation challenge test.

Exercise stress test.

You may also hear the tests called pulmonary function tests, or PFTs.

Lung function results are measured directly in some
tests and are calculated in others.

No single test can determine all of the
lung function values, so more than one type of test may be done. Some of the
tests may be repeated after you inhale medicine that enlarges your airways
(bronchodilator).

Spirometry

Spirometry is the most common lung function
test. It measures how much and how quickly you can move air out of your lungs.
You breathe into a mouthpiece attached to a machine called a spirometer. The machine records your results.

Spirometry can measure many different things about the way you breathe. These include how much air you can exhale, how much air you can breathe in and out in 1 minute, and the amount of air left in your lungs after a normal exhale.

Gas diffusion tests

Gas diffusion tests measure
the amount of
oxygen and other gases that move through the lungs' air sacs (alveoli) per minute.
These tests let you know how well gases are being absorbed into your blood from
your lungs. Gas diffusion tests include:

Carbon
monoxide diffusion capacity (also called DLCO). This test
measures how well your lungs transfer a small amount of carbon monoxide (CO)
into the blood. Two different methods are used for this test.

Single-breath or breath-holding method: You take a breath of air from a container. The air contains a very small amount of carbon monoxide. Measurements are taken as you breathe in.

Steady-state method: You do the same thing but measurements are taken as you breathe out.

Body plethysmography

Body plethysmography may be
used to measure:

Total lung capacity (TLC). This is the total amount of air
your lungs can hold. For this test, you sit inside a small airtight room. You breathe through a mouthpiece while pressure and air
flow measurements are collected.

Residual volume (RV). This is the
amount of air that remains in your lungs after you exhale as much as
you can. For this test, you sit inside the booth and breathe
while the pressure of the booth is monitored. You may need to breathe through a
mouthpiece while you are in the booth.

Inhalation challenge tests

Inhalation challenge tests are done to measure how your airways respond to substances that may be causing
asthma or wheezing. These tests are also called
provocation studies.

During
the test, you inhale increasing amounts of a substance through a
nebulizer. This is a device that uses a face mask or a mouthpiece to deliver the
substance in a fine mist (aerosol). Spirometry
readings are taken to evaluate lung function before, during, and after you inhale
the substance.

Exercise stress tests

Exercise stress tests
look at how exercise affects your lungs. Spirometry readings are
done after exercise and then again at rest.

Multiple-breath washout test

The multiple-breath
washout test is done to check people who have cystic fibrosis. For
this test, you breathe through a tube. First you breathe air that contains a tracer gas. Then you
breathe regular air while the amount of tracer gas you exhale is monitored.
Test results are reported as a lung clearance index (LCI). A high LCI value
means that the lungs are not working well.

Check the lungs of someone who is regularly
exposed to chemicals or other things that can damage the lungs.

Check how well treatments for lung diseases are working.

How To Prepare

Tell your doctor if you:

Have had recent chest pains or a
heart attack.

Take medicine for a lung
problem such as asthma. You may need to stop taking some medicines before
testing.

Are allergic to any medicines.

Have had recent
surgery on your eyes, chest, or belly, or if you have had a collapsed lung.

Do not eat a heavy meal just before this test. A full stomach may keep your lungs from fully expanding. You should not smoke
or do intense exercise for 6 hours before the test.

For the test,
wear loose clothing that doesn't restrict your breathing in any way.

Avoid food or drinks with caffeine. Caffeine can cause your
airways to relax and allow more air than usual to pass through.

If
you have dentures, wear them during the test. They help you form a tight seal
around the mouthpiece of the machine.

How It Is Done

Lung function tests are usually done in
special rooms that have all of the right equipment. The
test is usually done by a specially trained
respiratory therapist or technician.

For most of the
tests, you'll wear a nose clip to keep air from leaking through your nose. Then you'll breathe into
a mouthpiece connected to a recording device.

The exact steps depend on which test you have.
For example, you may be asked to inhale as
deeply as possible and then to exhale as fast and as hard as possible. You also
may be asked to breathe in and out as deeply and rapidly as you can for 15
seconds.

Some tests may be repeated after you have inhaled a spray containing
medicine that expands the airways in your lungs. You may be
asked to breathe a special mixture of gases, such as 100% oxygen, a mixture of
helium and air, or a mixture of carbon monoxide and air.

Sometimes a sample of
blood may be taken from an artery in your wrist to measure blood gases.

If you have body plethysmography, you will be asked to sit inside a small
enclosure. It's similar to a telephone booth, with windows that allow you to see out.
The booth measures small changes in pressure that occur as you breathe.

The accuracy of the tests depends on how well you can follow all of the
instructions. The therapist may ask you to breathe deeply during
some of the tests to get the best results.

The testing may take
from 5 to 30 minutes. It depends on how many tests are done.

How It Feels

If you have an arterial blood gas test,
you may feel some pain from the needle used to collect the blood. The other
lung function tests are usually painless. Some of the tests may be tiring for
people who have a lung disease.

You may cough or feel lightheaded
after breathing in or out rapidly, but you will be given a chance to rest
between tests. It may not be comfortable to wear the nose clip or to breathe through the mouthpiece.

If you have body plethysmography, you may feel uncomfortable in the
airtight booth. But the therapist will be nearby to open the door if you feel too uncomfortable.

If you are given
breathing medicine, it may cause you to shake or may increase your heart rate.
If you feel any chest pain or discomfort, tell the therapist right away.

Risks

For a healthy person, there's little or no risk in taking these tests. If you have a serious heart or lung condition, discuss your
risks with your doctor.

Results

Lung function tests check how well your lungs work. The tests can find lung problems, measure how serious they are, and check to see how well treatment for a lung
disease is working.

Most test results are available right away.

Normal

Results are in the normal range for a person with healthy lungs.

Abnormal

Test results are outside of the normal range for a person with healthy lungs. This may be a sign of some kind of lung disease. There are two main types of lung disease that can be found with lung function tests: obstructive and restrictive.

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